A method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal

Abstract

The invention relates to the technical field of molten iron smelting, and in particular to a method for solving the difficulty of slagging in converter smelting ultra-low silicon molten iron. The invention uses tundish slag to facilitate rapid slagging in the early stage of converter blowing, and facilitates low-temperature and efficient dephosphorization in the early stage; the tundish slag is an additional product inside the steel plant, has no cost impact, has objective direct economic benefits compared with the purchase and use of a composite slag-forming agent, can reduce the amount of light-burned dolomite added and the consumption of furnace protection refractory materials, and creates considerable direct economic benefits.

Description

Technical Field

[0001] The invention relates to the technical field of molten iron smelting, in particular to a method for solving the difficulty of slagging in converter smelting ultra-low silicon molten iron. Background Art

[0002] When the converter smelts low-silicon and low-manganese molten iron, compared with the converter smelting normal molten iron, the oxidation of silicon and manganese in the molten iron only takes 1-2 minutes, and the furnace enters the carbon-oxygen reaction period earlier. At this time, the decarburization rate is very high, and the blown oxygen and the iron oxide in the slag are used to participate in the decarburization reaction, so that the iron oxide component in the slag reaches the minimum value, and the low-melting point iron oxide component in the slag is reduced, resulting in a large amount of high-melting point dicalcium silicate generated and wrapped in lime, making it difficult to melt slag-forming agents such as lime and light-burned dolomite, which directly affects the dephosphorization effect. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a method for solving the difficulty of slag formation in converter smelting ultra-low silicon molten iron, and promotes slag formation of molten iron by precise parameter control in smelting operation. The specific technical scheme is as follows:

[0004] A method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal comprises the following steps:

[0005] 1) Prepare a clean slag pot filled with high-temperature slag for continuous casting, place it below the slag discharge port of the tundish, and keep it clean;

[0006] 2) According to the amount of slag in the tundish, the amount of molten steel in the tundish is adjusted, and the slag in the tundish is discharged from the slag discharge port and stored in the slag tank;

[0007] 3) After the slag pot is filled with tundish slag, it is hoisted to the slag turning yard by an overhead crane for turning;

[0008] 4) The turned-out tundish slag is crushed, screened, and dried to form a dry tundish slag finished product with a particle size of 10-40 mm; the tundish slag finished product is modified, and the specific operations are as follows:

[0009] A. Immerse the finished tundish slag in clean water 10-20 times its mass, add lanthanum chloride, stir for 20-30 minutes, add sodium hydroxide, stir for 20-30 minutes, and filter;

[0010] B. React the obtained filter residue in a hydrogen atmosphere at 600-700℃ for 3-5h, add boron powder to the reaction product, and sinter it at 800-900℃ under vacuum for 7-9h to obtain modified slag:

[0011] 5) Using a feeding belt, the modified ladle slag is mixed with the finished tundish slag of step (4) and transported to the high-level silo of the converter;

[0012] 6) When the converter is smelting low-silicon hot metal, after the ignition is successfully started, the first batch of slag-making materials is added from the high-level silo, and then 500kg of tundish slag is added;

[0013] 7) The converter blowing process adopts a high lance position operation mode, and the lance position is gradually reduced from 1800mm at the start of blowing to the final carbon pulling lance position;

[0014] 8) Steel is tapped directly at the end of smelting.

[0015] Furthermore, in step (1), the slag pot has a capacity exceeding 3 tons.

[0016] Furthermore, in step (4), the amount of lanthanum chloride used is 0.22-0.23% of the mass of the finished tundish slag.

[0017] Furthermore, in step (4), the amount of sodium hydroxide used is 3-5% of the mass of the finished tundish slag.

[0018] Furthermore, in step (4), the amount of boron powder used is 0.1-0.3% of the mass of the finished tundish slag.

[0019] Furthermore, in step (5), the mass ratio of the modified ladle slag to the intermediate ladle slag product is 1:150-200.

[0020] Furthermore, in step (8), the direct steel tapping method is any one of one-time pouring or non-turning.

[0021] Compared with the prior art, the technical effects of the present invention are embodied in:

[0022] In the continuous casting process of the molten steel in the continuous casting tundish of the present invention, the slag above the molten steel in the tundish is discharged through the slag discharge port to control the cleanliness of the molten steel. The formation of the continuous casting tundish slag is mainly due to the slag in the ladle entering the tundish at the end of the molten steel casting, and secondly, the molten steel corrodes the refractory material of the tundish. Through chemical analysis of the tundish slag, it is found that it contains a large amount of fast slag-forming components, such as SiO2, Al2O3, MnO, etc., which are recycled and used. When the converter smelts low-silicon molten iron, adding the tundish slag can promote slag formation and solve the problem of difficult slag formation.

[0023] The present invention utilizes the characteristics of high SiO2, Al2O3 and MnO in tundish slag and uses it when smelting low-silicon molten iron in a converter to increase SiO2, MnO, Al2O3 and the like in the slag to promote slag formation.

[0024] 1) The use of tundish slag is conducive to rapid slag formation in the early stage of converter blowing, and is conducive to low-temperature and efficient dephosphorization in the early stage;

[0025] 2) Tundish slag is an additional product within the steel plant, with no cost impact, and has objective direct economic benefits compared with the purchase and use of composite slag-reducing agents;

[0026] 3) The present invention increases the use of rare earth lanthanum and boron by modifying the tundish slag, so that the molten steel has high integrity, is more stable as a whole, is easy to separate from impurities, and the slag removal process is efficient and fast;

[0027] 4) The tundish slag contains MgO, which can promote the rapid slagging of the converter and increase the MgO content in the slag, thereby improving the furnace protection effect, reducing the amount of light-burned dolomite added and the consumption of furnace protection refractory materials, and creating considerable direct economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Gun position control parameter diagram. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0030] Example 1

[0031] A method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal comprises the following steps:

[0032] 1) Prepare a clean slag pot filled with high-temperature slag for continuous casting, place it below the slag discharge port of the tundish, and keep it clean; the capacity of the slag pot should exceed 3 tons;

[0033] 2) According to the amount of slag in the tundish, the amount of molten steel in the tundish is adjusted, and the slag in the tundish is discharged from the slag discharge port and stored in the slag tank;

[0034] 3) After the slag pot is filled with tundish slag, it is hoisted by an overhead crane to the slag turning yard for turning;

[0035] 4) The turned-out tundish slag is crushed, screened, and dried to form a dry tundish slag product with a particle size of 10 mm; the tundish slag product is modified, and the specific operations are as follows:

[0036] A. Immerse the finished tundish slag in clean water 20 times its mass, add lanthanum chloride, stir for 30 minutes, add sodium hydroxide, stir for 20 minutes, and filter;

[0037] B. The obtained filter residue is reacted in a hydrogen atmosphere at 700°C for 5 hours, boron powder is added to the reaction product, and sintered at 900°C under vacuum for 7 hours to obtain the modified slag:

[0038] The amount of lanthanum chloride used is 0.23% of the mass of the finished tundish slag, the amount of sodium hydroxide used is 3% of the mass of the finished tundish slag; the amount of boron powder used is 0.3% of the mass of the finished tundish slag;

[0039] 5) using a feeding belt to mix the modified ladle slag with the finished tundish slag of step (4), and transporting them to the high-level silo of the converter; the mass ratio of the modified ladle slag to the finished tundish slag is 1:200;

[0040] 6) When the converter is smelting low-silicon hot metal, after the ignition is successfully started, the first batch of slag-making materials is added from the high-level silo, and then 500kg of tundish slag is added;

[0041] 7) The converter blowing process adopts a high lance position operation mode, and the lance position is gradually reduced from 1800mm at the start of blowing to the final carbon pulling lance position;

[0042] 8) Directly tapping steel at the end point of smelting; the direct tapping method is one-time pouring.

[0043] Example 2

[0044] A method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal, taking the production of HRB400E steel as an example, comprises the following steps:

[0045] To produce HRB400E steel, after the slag splashing and furnace protection of the converter are completed, 10.1t of scrap steel and 89.5t of molten iron are added successively, of which the silicon content of the molten iron is 0.065%, the phosphorus content is 0.130%, and the carbon content is 3.7%. The temperature is 1330℃, and then the oxygen lance is lowered for oxygen smelting. The opening gun position is controlled at 1800mm for ignition. After successful ignition, 1210kg of lime and 500kg of light-burned dolomite are added first. After smelting for 20s, 505kg of finished tundish slag and 1.7kg of modified ladle slag are added. The oxygen flow rate is controlled at 21000Nm3 / h throughout the process. Judging by the flame and slag jumping of the converter mouth, slag is generated when smelting reaches 3.1min. At this time, the second batch of slag-making materials is added, 500kg of lime is added first, and 295kg of light-burned dolomite is added after smelting for 20s. The gun position is controlled at 1710mm. After smelting for 4.5 minutes, 200 kg of lime and light burning were added, and the gun position was controlled at 1600 mm. After smelting for 5.5 minutes, the gun position began to be gradually reduced in a step-like manner. At smelting for 9.4 minutes, it was reduced to 1.1 m of the carbon pulling gun position. When carbon pulling was 0.8 minutes, the temperature and carbon content of the molten steel were judged to meet the target requirements by observing the flame at the furnace mouth and using the TCO probe for online temperature measurement. At this time, the oxygen gun was raised, and the steel was directly tapped according to the non-inverted furnace tapping organization. The furnace was shaken to the back of the furnace for tapping. The molten steel temperature was measured at the back of the furnace at 1637 ° C. The carbon content of the molten steel sample in the furnace was 0.10% and the phosphorus content was 0.022%, as shown in Attached Table 2. The preparation of modified tundish slag was the same as in Example 1.

[0046] After using the tundish slag, the converter slagging effect is greatly improved, and the direct smelting process can be operated at a low gun position and a large flow rate. The converter pure oxygen supply time and dephosphorization rate are completed at 10.2 minutes and 83.1% respectively, and the overall control is good. The end point achieves carbon pulling and steel production, and the converter condition is maintained. Other operations are the same as in Example 1.

[0047] Example 3

[0048] A method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal, taking the production of HRB400E steel as an example, comprises the following steps:

[0049] To produce HRB400E steel, after the slag splashing and furnace protection of the converter is completed, 9.7t of scrap steel and 90.2t of molten iron are added successively, of which the silicon content of the molten iron is 0.058%, the phosphorus content is 0.135%, and the carbon content is 3.9%. The temperature is 1325℃, and then the oxygen lance is lowered for oxygen smelting. The lance position is controlled at 1820mm for ignition. After successful ignition, 1110kg of lime and 490kg of light-burned dolomite are added first. After smelting for 18s, 500kg of finished tundish slag and 2.3kg of modified tundish slag are added. The oxygen flow rate is 21000Nm throughout the process. 3 / h control. Judging by the flame and slag jumping at the converter mouth, slag was generated when smelting reached 3.3min. At this time, the second batch of slag-making materials was added. 450kg of lime was added first, and 300kg of light-burned dolomite was added after smelting for 22s. The gun position was controlled to 1700mm. Smelting to 4.8min, 200kg of lime and light-burned dolomite were added, and the gun position was controlled to 1600mm. Smelting to 5.9min, the gun position began to gradually decrease in a step-like manner. When smelting to 9.6min, it was reduced to 1100mm for the carbon pulling gun position. When carbon was pulled for 0.7min, the flame at the furnace mouth was observed to judge that the molten steel temperature and carbon content reached the target requirements. At this time, the oxygen gun was raised to measure the temperature of the furnace and sample the temperature. The molten steel temperature was measured to be 1643℃, and then the steel was tapped. The molten steel sample in the furnace was analyzed for carbon content of 0.09% and phosphorus content of 0.020%, as shown in Attached Table 2. The preparation of modified tundish slag is the same as in Example 1.

[0050] After using the tundish slag, the converter slagging effect is greatly improved, and the direct smelting process can be operated at a low gun position and a large flow rate. The converter pure oxygen supply time and dephosphorization rate are completed at 10.3 minutes and 85.2% respectively, and the overall control is good. The end point achieves carbon pulling and steel production, and the converter condition is maintained. Other operations are the same as in Example 1.

[0051] Example 4

[0052] To produce HRB400E steel, after the slag splashing and furnace protection of the converter is completed, 10.2t of scrap steel and 90.1t of molten iron are added successively, of which the silicon content of the molten iron is 0.062%, the phosphorus content is 0.133%, and the carbon content is 3.6%. The temperature is 1324℃, and then the oxygen lance is lowered for oxygen smelting. The opening gun position is controlled at 1830mm for ignition. After successful ignition, 1180kg of lime and 500kg of light-burned dolomite are added first. After smelting for 22s, 500kg of finished tundish slag and 1.9kg of modified tundish slag are added. The oxygen flow rate is 21000Nm throughout the process. 3 / h control. Judging by the flame and slag jumping at the converter mouth, slag was generated when smelting was 3.2min. At this time, the second batch of slag-making materials was added. 460kg of lime was added first, and 280kg of light-burned dolomite was added after smelting for 25s. The gun position was controlled to 1710mm. Smelting to 4.7min, 200kg of lime and light-burned dolomite were added, and the gun position was controlled to 1610mm. Smelting to 5.8min, the gun position began to gradually decrease in a step-like manner, and it was reduced to 1100mm at the carbon pulling gun position when smelting to 9.2min. When carbon was pulled for 0.7min, by observing the flame at the furnace mouth and using the TCO warhead for online temperature measurement, it was judged that the molten steel temperature and carbon content reached the target requirements. At this time, the oxygen gun was raised to directly tap the steel to the rear of the furnace without tilting the furnace. The molten steel temperature was measured at the rear of the furnace at 1641℃. The molten steel sample in the furnace was analyzed to have a carbon content of 0.10% and a phosphorus content of 0.019%, as shown in Attached Table 2. The preparation of modified tundish slag is the same as in Example 1.

[0053] After using the tundish slag, the converter slagging effect is greatly improved, and the direct smelting process can be operated at a low gun position and a large flow rate. The converter pure oxygen supply time and dephosphorization rate are completed at 9.9 minutes and 85.7% respectively, and the overall control is good. The end point achieves carbon pulling and steel production, and the converter condition is maintained. Other operations are the same as in Example 1.

[0054] Comparative Example:

[0055] To produce HRB400E steel, after the slag splashing and furnace protection of the converter, 9.9t of scrap steel and 89.7t of molten iron were added, of which the silicon content of the molten iron was 0.063%, the phosphorus content was 0.132%, and the carbon content was 3.7%. The temperature was 1326℃. After adding iron, the oxygen lance was lowered for oxygen smelting. The lance position was controlled at 1830mm for ignition. After successful ignition, 1100kg of lime and 450kg of light-burned dolomite were added first, and the oxygen flow rate was controlled at 19000Nm3 / h throughout the process. Judging from the flame and slag jumping at the converter mouth, the first batch of slag was added and slag was not produced after 4 minutes of smelting. At this time, the oxygen flow rate was adjusted to 18000Nm3 / h to continue smelting at a high gun position. Slag was produced at 6.6 minutes of smelting. At this time, the second batch of slag-making materials was added, and 500kg of lime was added first. After 30 seconds of smelting, 200kg of lightly burned dolomite was added, and the gun position was still controlled at 1830mm. Due to the poor slag removal effect during the smelting process, continuous drying was continued. The smelting was still controlled at a high gun position until 11.2 minutes. The slag removal effect was improved by the flame at the furnace mouth at 11.7 minutes, but the carbon content was already low. At this time, the gun position was immediately reduced from 1830mm to 1100mm carbon pulling gun position. After 0.5 minutes of carbon pulling, the molten steel temperature was judged to be appropriate by the flame at the furnace mouth, but the molten steel was relatively over-oxygenated. After using the TCO warhead to measure the temperature online, the oxygen lance was taken out and the furnace was turned over for temperature measurement and sampling. The molten steel temperature was measured to be 1636℃. The carbon content of the molten steel sample in the furnace was 0.05% and the phosphorus content was 0.050%. See Appendix 2 for details.

[0056] No tundish slag was used, and slagging was difficult in the converter smelting process. Low flow and high gun position were used throughout the process, resulting in poor dynamic conditions and low oxygen utilization. The converter pure oxygen supply time and dephosphorization rate were 12.2 minutes and 62.1% respectively. The phosphorus content in the final molten steel did not meet the national standard requirements, and the molten steel was severely overoxidized, making it difficult to maintain the converter condition.

[0057] Table 1 Composition of molten iron

[0058] C / % Si / % Mn / % P / % S / % V / % Ti / % Temperature / ℃ Loading amount / t Example 2 3.70 0.065 0.042 0.130 0.045 0.025 — 1330 99.6 Example 3 3.90 0.058 0.035 0.135 0.040 0.019 — 1325 99.9 Example 4 3.60 0.062 0.036 0.133 0.047 0.022 — 1324 100.3 Comparative Example 3.70 0.063 0.040 0.132 0.043 0.024 — 1326 99.6

[0059] It can be seen from the table that before entering the furnace, the actual composition differences between the groups were not significant, and the parameter changes in actual operation were small, which met the comparison conditions.

[0060] Table 2 End point control

[0061] C / % P / % Dephosphorization rate / % Temperature / ℃ Oxygen supply time / min Example 2 0.10 0.022 83.1 1637 10.2 Example 3 0.09 0.020 85.2 1643 10.3 Example 4 0.10 0.019 85.7 1641 9.9 Comparative Example 0.05 0.050 62.1 1636 12.2

[0062] It can be seen from the table that the dephosphorization rates of Examples 2-4 operated according to the present invention all meet the requirements.

Claims

1. A method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal, characterized in that: The following steps are involved: 1) Prepare a clean slag pot filled with high-temperature slag for continuous casting, place it below the slag discharge port of the tundish, and keep it clean; 2) According to the amount of slag in the tundish, the amount of molten steel in the tundish is adjusted, and the slag in the tundish is discharged from the slag discharge port and stored in the slag tank; 3) After the slag pot is filled with tundish slag, it is hoisted to the slag turning yard by an overhead crane for turning; 4) The turned-out tundish slag is crushed, screened, and dried to form a dry tundish slag finished product with a particle size of 10-40 mm; the tundish slag finished product is modified, and the specific operations are as follows: A. Immerse the finished tundish slag in clean water 10-20 times its mass, add lanthanum chloride, stir for 20-30 minutes, add sodium hydroxide, stir for 20-30 minutes, and filter; B. The obtained filter residue is reacted in a hydrogen atmosphere at 600-700°C for 3-5h, boron powder is added to the reaction product, and sintered at 800-900°C under vacuum for 7-9h to obtain a modified slag; The amount of lanthanum chloride used is 0.22-0.23% of the mass of the finished tundish slag; the amount of sodium hydroxide used is 3-5% of the mass of the finished tundish slag; the amount of boron powder used is 0.1-0.3% of the mass of the finished tundish slag; 5) Using a feeding belt, the modified ladle slag is mixed with the finished tundish slag of step (4) and transported to the high-level silo of the converter; 6) When the converter is smelting low-silicon hot metal, after the ignition is successfully started, the first batch of slag-making materials is added from the high-level silo, and then 500kg of the finished tundish slag is added; 7) The converter blowing process adopts a high lance position operation mode, and the lance position is gradually reduced from 1800mm at the start of blowing to the final carbon pulling lance position; 8) Steel is tapped directly at the end of smelting.

2. The method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal according to claim 1, characterized in that: In step (1), the slag pot has a capacity of more than 3 tons.

3. The method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal according to claim 1, characterized in that: In step (5), the mass ratio of the modified ladle slag to the intermediate ladle slag finished product is 1:150-200.

4. The method for solving the difficulty of slagging in converter smelting ultra-low silicon hot metal according to claim 1, characterized in that: In step (8), the direct steel tapping method is either one of one-time pouring or non-turning.

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